Conventionally, there is known a technique for purifying exhaust gas from a diesel engine, in which a case including a diesel particulate filter (hereinafter referred to as a DPF case) and a case including a urea selective reduction catalyst (hereinafter referred to as an SCR case) are disposed as an exhaust gas purifier (exhaust gas post-processing device) in the exhaust path of the diesel engine, and the exhaust gas is guided into the DPF case and the SCR case (see, for example, Patent Documents 1 to 3).